This invention relates to method and apparatus for charging batteries and providing for terminating the charging of a battery in order to reduce the likelihood of damage to it. The invention, although not so limited, has particular application to the charging of nickel cadmium batteries, and in this application provides the least likelihood of excessive heat and pressure buildup occurring within the cells of the battery while still achieving a full charge.
It is known from the prior art that in order to remove possible imbalances amoung battery cells they can be discharged individually. Such discharging additionally tends to eliminate the "memory" effect common to such batteries. Certainly, a feature such as this one could be added to the invention described herein.
In addition it is known that it is desirable to terminate charging of a nickel cadmium battery upon the occurrence of a zero or negative rate of change of battery or cell voltage with respect to time. The art describes apparatus by which this occurrence can be sensed and charging terminated. In operating in this manner, however, it is required that the battery be vented or in the case of sealed cells be constructed to withstand high internal pressures while having the capability of maintaining a high rate of chemical recombination. High pressures and elevated temperatures occur in sealed nickel cadmium cells near the end of a fast charging cycle. During this period only a small percentage of additional charge is stored, and the balance will simply be dissipated as heat.
It is therefore an object of this invention to provide means and method for charging batteries which will permit the charging cycle to be terminated prior to a point where there would be a substantial increase in temperature or pressure within the cells of the battery.
It is another object of this invention to provide means and method for charging batteries which will permit charging at a relatively rapid rate those batteries which might be designated as "slow charge" batteries.
Another object of this invention is to provide means and method for charging nickel cadmium batteries at a high rate while providing the capability of terminating the charging substantially before the battery fully enters its "gas" phase.